The subject disclosure is directed to fluid filtration, and particularly, to a bag-type filter assembly having two concentric circumferentially pleated media sleeves defining an annular passage therebetween, which receives fluid for filtration, and more particularly to apparatus and methods for forming filter sleeves having circumferential pleats.
Bag-type filter systems for fluid filtration are well known in the art. These systems typically include a cylindrical housing, which is closed at one end and has a removable cover at the opposed end. An inlet conduit delivers fluid to be filtered into the housing and an outlet conduit removes filtered fluid from the housing.
Replaceable bag filters are disposed within the housing in order to filter fluids delivered thereto. Typically, bag filters include filter media having an open upper end and a closed bottom. The filter bag is supported within an open mesh basket or cage, which is typically suspended within the housing. The basket is intended to support the media of the filter bag to prevent it from bursting as the bag fills with liquid.
There have been a number of efforts to design pleated filters and machines for fabricating the same. For example, U.S. Pat. No. 5,543,047 to Stoyell et al. (hereinafter Stoyell et al.) describes filter elements employing an over-laid pleat or angled pleat media configuration and methods to produce said configuration. Stoyell et al. describe a pusher-bar pleating method, creating a slanted pleat wherein “the two legs of each pleat have differing heights prior to being formed into a laid-over state”. During the Stoyell et al. process, flexible media sits flat upon a horizontal surface while a pusher bar exerts a vertical pressure on the media while also moving in the forward direction. The flexible media “balloons” off the horizontal surface in a predictable manner while the pusher bar continues to push the media beneath a stationary pressure plate where heat and pressure set the pleat. An additional blade is engaged behind each pleat to prevent blowback of the pleat pack. An optional feature is described wherein a third knife is stationed beneath the horizontal surface and advances upward beneath the media to better encourage the media to “balloon” during forward movement of the pusher bar. Each new pleat is predictably creased as the new pleat is pressed between the face of the pusher bar and previously pleated material under the pressure plate.
Entire pleat packs are advanced beneath the pressure plate one pleat at a time with each forward advancement of the pusher bar. The pleat formation is governed by the face angle of the pusher bar, the travel distance of the pusher bar and relative positions and angles of the other tools and fixtures. The resulting pleat pattern is described as arcuate or slanted pleats in intimate contact at an angle between 15° and 75° relative to the tangent of the circumference of the cartridge core. In one embodiment, the pleat orientation is maintained by a strip of webbing adhered and spirally wrapped around the circumference and extending the entire length of the element. The spiral wrap is spaced so as not to impede flow.
A filter manufactured in accordance with the Stoyell et al. patents is manufactured by Pall Corporation of East Hills, N.Y., and sold under the tradename Ultipleat.® One version of this product is the Ultipleat® High Flow filter, which is manufactured in several different sizes. For example, the filter is manufactured in 6 inch, single open-ended configuration with a 20 inch, 40 inch or 60 inch height. The Pall Ultipleat® filter is also available as a standard 10 inch cartridge with a 2.5 inch diameter. In this format, several 10 inch cartridges may be stacked together for certain applications.
For another example, U.S. Pat. No. 5,174,896 to Harms, II (hereinafter Harms, II) describes a method of forming a slanted pleat pattern, resulting in a pleat style similar to that described in Stoyell et al. Harms, II, however utilizes driven rollers and one roller with a scoring means. Flat media is pulled between a driven rubber impact roller and a pleater roller fitted with scoring wires under controlled pressure. The scoring wires in conjunction with the impact roller exert a more concentrated force on the media in a controlled location. The result is a weakened or compressed zone traversing the width of the media roll. A second set of rollers push the scored media forward against what is described as an advancement barrier, which encourages the media to buckle and fold along the scored compressed zones. The pleat formation is governed by the spacing of the scoring wires on the pleater roller. A pattern of alternating short and long distances between scoring wires will result in a pleat with one leg longer than the other, generating the slanted pleat orientation.
For still another example, U.S. Pat. No. 2,395,449 to Briggs (hereinafter Briggs) describes a filter element with pleats in close contact and arcuate or angled in nature contained by a binding strip. Briggs describes a method of maintaining pleats of a filter element in close contact and slanted. A strip of net-like backing or binding material adheres to the tips of a compressed pleat pack on one side of the pleat pack. This bound surface becomes the inner diameter of the pleated element as the pleat pack is formed into a cylinder. At this point, the filter element resembles a radially pleated element. Additional processing of the filter element, including rotational friction along the element outer diameter, creates the spiral pleat pattern, which may then be bound by an additional strip of net-like backing or binding material.
In still another example, U.S. Pat. Nos. 5,882,288 and 6,048,298 to Paul et al. (hereinafter Paul et al.) describe an apparatus to form spiral pleated filter cartridges. Paul et al. describe an apparatus designed to transform a radially pleated filter of an initial outer diameter into a spirally pleated filter of lesser final diameter. Similar to that described in Briggs, the apparatus imparts a rotational friction and compression along the outer diameter and creates the spiral pleat pattern. The pleat pattern is maintained due to friction with a snug fitting outer netting or plastic cage, which is inserted over the cylindrical pleat pack while compressed within the apparatus.
Different particularly useful machinery is capable of producing a pleat already in the laid-over state. A common technique utilizes a pusher bar or a set of pushing blades and a set of gripping rollers or gripping belts. Much like Stoyell et al., the pusher bar creates a “ballooning” of the media, then wedging the ends of the “ballooned” media into the grips of the gripping rollers. The gripping rollers advance and set a crease in the “ballooned” media under pressure and, in some cases, heat. The pleat pattern produced resembles that desired to form a circumferentially pleated filter element. Pleat formation is governed by the distance that the pusher bar advances and the relative drive speed of the gripping rollers. Often the drive of the pleater is described as a ratcheting motion or intermittently driven, where the drive tooling is designed to advance the gripping rollers a set fraction of a revolution for each advancement of the pusher bar. Some embodiments also include additional knife blades which aid in the “ballooning” of the media, similar to Stoyell et al., and also create minor variations of this flattened pleat pattern.
For the most part, these prior art efforts have fallen short in that the prior art pleating mechanisms are extremely specialized. The machine hardware is specifically designated to generate a pleat of particular height, angle, and degree of overlap. For example, to create standard radial pleats with Harms, II, an operator must change the location of the scoring wires so that the scoring wires are equally spaced around the circumference of the pleater roller or change to an entirely different roller all together. In addition, it has been demonstrated that this method of pleating is less successful when pleating polymeric or meltblown media, which is less prone to score. Excess pressure is necessary to create the desired effect, which leads quickly to worn out tooling, such as loose or stretched scoring wires. The noise from such operation is also described as unbearable.
Further, U.S. Pat. No. 297,240 to Liebeskind (hereinafter Liebeskind) describes a method of applying an adhesive tape on top a pleated pattern. Pleater pusher knives create the media “ballooning” upstream of gripping rollers. Just past the pusher knives and just before the gripping rollers, a narrow strip of adhesive tape is applied and fastened to the media. The adhesive tape functions the locally adhere and retard the advancement of the lateral pleat and create a counter-pleat referred to as a cusp. The pleated/counter-pleated material and the adhered tape undergo a heat cycle to permanently set the pleat pattern. The adhesive tape is then removed. Liebeskind relates more closely to the garment industry, where a counterpleat is created for aesthetic appeal. The tape is a mere temporary medium to create this effect. No benefits of counterpleating within the scope of filtration are currently recognized.
U.S. Pat. No. 3,349,159 to Luboshez (hereinafter Luboshez) describes a method of applying release paper to each side of the pleat pack, resulting in a sandwiched pleat pack. The release paper holds and protects the pleated media as it undergoes a heat cycle to set the pleats. Then, the release paper is removed. The resulting pleat pattern is a series of laid-over pleats extending laterally the width of the media. Like Liebeskind, Luboshez is in the field of the garment industry, where the pleated media is woven and sensitive to scorching at the temperatures experienced during processing.
U.S. Pat. No. 3,390,218 to Painter et. al (hereinafter Painter et al.) describes a method of pleating media utilizing sets of rollers. A set of vertically stacked double rollers create a feed nip to push material into what is described as a compression zone. This zone is confined vertically by moveable pressure plates or other fixturing and a downweb retarder roll, which rotates at a speed slower than the initial set of rollers to create a crumpling of media in the compression zone. The crumpled media eventually passes between the retarder roll and the bottom roller of the feed nip to create an exit nip. The pleats are laid over or compressed into what are described as micropleats in patterns which may be varied cross-web, if so desired, depending on circumferential grooves on the top upstream stacked roller. Pleat height and orientation are determined by roller speeds relative to one another, circumferential groove pattern, and pressure plate position within the compression zone. One embodiment of this invention creates a puckered pleat pattern, where a small pleat and a large pleat alternate in pattern down web as well as cross web. In cross-section, however, this puckered pleat resembles a “W’ pleat in a partially laid-over position. In Painter et al, the control of overlap is irregular. The overlap depends entirely on the crumple characteristics of non-scored media in the compression zone. The vertically stacked rollers and compression zone cannot affect the media grip from the retarder roller. Further, the machine of Painter et al. also produces highly specialized pleats and would not be able to produce standard radial pleats without substantial machine alterations. As can be seen from above, there are several disadvantages associated with existing pleating machinery.